An example type of fired equipment, a steam generator utilizes a heat source to convert a liquid-phase fluid (e.g., water) to a gaseous-phase fluid (e.g., steam). In one implementation, the steam generator construction includes one or more tubes through which the fluid is pumped under pressure. The fluid tubes pass through the steam generator in a manner that transfers heat from the heat source to the fluid within the tubes. The fluid vaporizes into pressurized saturated steam within the fluid tubes and is discharged from the steam generator. The pressurized steam or other heated fluid can then be used for power generation (e.g., via a steam turbine), heating (e.g., via a heat tracing system, a heat exchanger, and/or a radiator), enhanced oil recovery (EOR, e.g., steam injection), for example. The heat source can be derived from combustion of one or more fuels (e.g., coal, oil, produced gas, waste gas, natural gas, propane, biomass, etc.), for example.
In various implementations, the fluid flow rate through the tubes is adjustable, according to the quantity of steam desired. Further, the burner heat output may also be adjusted to maintain a constant working temperature within the steam generator or a desired steam quality output from the steam generator. Still further, the burner output may be varied based on the flow rate of fluid being pumped through the fluid tubes. Thus, the burner output may be adjusted by open-loop or closed-loop control using the fluid throughput and/or measured temperature within the steam generator as control variables, for example.
Steam generators often include different sections that use different fluid tube arrangements depending on the primary mode of heat transfer intended for that particular section. For example, a radiant section may position the fluid tubes in line-of-sight with the heat source (e.g., a flame), but not directly in the flame because the high localized flame temperature may exceed the yield strength of the fluid tubes. Further, a convection section may position the fluid tubes directly in the flow path of the combustion gases downstream of the flame in order to maximize radiant and convective heat transfer of combustion gases to the fluid tubes. A target wall provides a distinct transition point from the radiant section and the convection section.
Effective transitions between different sections of a steam generator may be difficult to achieve due to the differing requirements of the different sections of the steam generator. Further, manufacturing and assembly challenges have previously limited the scope of options available for shaping effective transitions between different sections of the steam generator.